Psv Sizing Calculation Spreadsheet 291r31

GAS/VAPOR & STEAM RELIEF SIZING CALCULATION Calculation according API-RP-520 7th edition, January 2000)

API STD 520 eight edition, Dec 2008, Example1

Accumulation Accumulated press. (P1)

RELIEF VALVE ORIFICE CALCULATION X VAPOR / GAS O Check for subcritical flow

P X

2 k +1

( )

≥

Calculated Kn with

K n=

Critcal flow vapor/gas

A=

O

√

131. 6⋅W T⋅Z ⋅ C⋅K d⋅P1⋅K b⋅K c M

Calculated C with

√

1 . 904⋅W P1⋅K d⋅K b⋅K c⋅K n⋅K sh

A=

k k −1

2 k +1

( )

C=520⋅ k⋅

k+1 k−1

K-VALUES

Napier correction factor (Kn) Superheat steam cor. factor (Ksh)

NOTES :

2. 764⋅P1−1000 3. 324⋅P1 −1061

Subcritical flow vapor/gas

A=

√

0 .179⋅W T⋅Z ⋅ F 2⋅K d⋅K c M⋅P1⋅( P1 −P2 )

Calculated F2 with

F2 =

STANDARD ORIFICE AREAS (acc. API-RP-526) Orifice tag D E F 71 126 198 Area (mm²) 0,110 0,196 0,307 Area (sq. inch) CORRECTION FACTORS Discharge coefficient (Kd) Back pressure coeff. (Kb) Comb. Rupture disk factor (Kc)

Fluid Vapor-gas / Steam relief (V / S) Relieving temperature (T) (°C) Molweight gas/vapor (M) Compressibility (Z) (@ relief cond.) Specific heat ratio /cv (k) (kg/h) Required relief load (W)

STEAM only in case of steam relief

Check for subcritical flow using the following formula

P2

PROCESS DATA

HP-flare 5.17 1.00 10.00 6.70

(barg) (bara) (%) (bara)

√(

(

k 1−r (k−1) /k ⋅(r)2/k⋅ k−1 1−r

)

)

Abbr. A W C T Z M P1 P2 F2 k r Kd Kb Kc Kn Ksh

Vapor V 75 51.00 0.90 1.11 24270.0

Description Calculated orifice area Required mass flow k-value coefficient Relieving temperature Compressibility factor Mol weight Upstream relieving pressure Back pressure Coefficient subcritical flow Specific heat ratio /Cv Pressure ratio (P2/P1) Discharge coefficient Back Pressure Coefficient Combination correction factor Napier correction factor Superheat correction factor

unit mm² kg/hr K kg/kmole bara bara

G

H

J

K

L

M

N

325 0,503

506 0,785

830 1,287

1186 1,838

1841 2,835

2323 3,600

2800 4,340

0.975 1.0 1.0

CALCULATED ORIFICE Type of flow k-value coefficient (C) Coefficient subcritical flow (F2)

1.0

Calculated orifice Recommended orifice Orifice TAG (acc API-RP-526)

CALC. DATA

VALVE DATA

RELIEF VALVE DATA Discharge to Set pressure (Pset) Back pressure (P2)

(mm²) (mm²)

Critical 328 3697

4116 P

mm² kg/hr K kg/kmole bara bara

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